1. Field
The present invention relates to new cure accelerator systems for anaerobic curable compositions. These anaerobic cure systems include tetraalkyl ammonium oxidizing salts that are soluble in the (meth)acrylate component of the composition.
2. Brief Description of Related Technology
Anaerobic adhesive compositions generally are well-known. See e.g., R. D. Rich, “Anaerobic Adhesives” in Handbook of Adhesive Technology, 29, 467-79, A. Pizzi and K. L. Mittal, eds., Marcel Dekker, Inc., New York (1994), and references cited therein. Their uses are legion and new applications continue to be developed.
Conventional anaerobic adhesives ordinarily include a free-radically polymerizable acrylate ester monomer, together with a peroxy initiator and an inhibitor component. Oftentimes, such anaerobic adhesive compositions also contain accelerator components to increase the speed with which the composition cures.
The peroxy initiator is oftentimes cumene hydroperoxide (“CHP”). CHP has a distinctive odor, which to some people is found to be objectionable. Even when formulated into anaerobic adhesives, the odor is said to still be noticed by those people finding it objectionable.
Efforts have been made to seek alternatives to CHP. For instance, U.S. Pat. No. 3,980,627 (McDowell) is directed to and claims an anaerobic sealant composition having an extended shelf life in the presence of air and capable of polymerization upon exclusion of air. The composition includes a polyacrylic ester monomer represented by a certain formula; an inorganic salt as the sole polymerization initiator (and selected from ammonium perchlorate, alkali metal perchlorate, alkaline earth metal perchlorate, ammonium persulfate, alkali metal persulfate, and alkaline earth metal persulfate), present in an amount sufficient to initiate polymerization of the monomer in the absence of air; an accelerator present in an amount sufficient to accelerate polymerization of the monomer in the absence of air; and a polymerization inhibitor in an amount sufficient to retard polymerization of the monomer during storage of the composition in the presence of air.
In the '627 patent, it is suggested that the inorganic salt initiator is insoluble in the polyacrylate ester monomer and thus heating is suggested to influence its solubility. Even after heating, some of the salt remains undissolved. Thus, prior to use of the composition as an adhesive, filtration or decantation is performed. More specifically, column 3, line 58-column 4, line 17 of the '627 patent reads:                The anaerobic sealant compositions are compounded by first admixing predetermined amounts of the polyacrylate ester monomer and the inorganic salt initiator. Thereafter the accelerator is added, and the resulting admixture is aged until anaerobic properties are developed. If desired, a portion of the inorganic salt initiator to be added to the composition can be first dissolved in the accelerator and then added to the monomer as a solution.        Aging of the prepared admixture can be carried out at room temperature or above. The necessary aging period depends to some extent on the aging temperature since anaerobic properties are developed in the formulation within a relatively shorter time period at elevated temperatures. Aging temperatures up to about 200° F. are suitable. At ambient temperature the compounded formulations preferably are aged for at least about 2 days. At elevated temperatures, for example, at about 120° F., the formulations preferably are aged about 1 day. After aging, any solid materials present in the produced anaerobic composition are filtered out or otherwise removed, e.g., by centrifuging and decanting the composition.        
Recently, CHP has come under regulatory scrutiny in certain jurisdictions in which anaerobic adhesives are marketed and sold.
In an effort to passivate that regulatory scrutiny, Henkel Corporation has invested time and energy to design and develop new alternative anaerobic cure systems. One such way is the subject of this disclosure, and is described below.